Liquid meters used in the trade of goods are often calibrated and tested for accuracy using vessels of known volume, commonly known as open neck provers. Open neck provers are made of metal and are typically comprised of a narrow upper neck that features a sight glass and scale plate and is attached to a tank body made up of a downwardly expanding top cone, a cylindrical body, a downwardly contracting lower cone complete with a drain assembly and valve. The drain may be placed concentrically at the lowest point of the bottom cone, or the cone may be eccentric in nature and the drain located other than at the center of the tank, which is known within the field as a French Drain.
Examples of such conventional open neck provers are shown in U.S. Pat. No. 2,742,789 and U.S. Pat. No. 3,040,558, where the tank body has a conical bottom wall with a central drain. One drawback of such conventional designs is the creation of vortices during draining of the tank, which is believed to contribute to the significant drain time required to empty such a tank. While a French Drain is known to reduce the drain time for a given tank size, applicant has developed a new open neck prover design that offers another alternative to the conventional center drain and offset French Drain.